Recently, track traveling vehicles with linear motors as an urban transportation system have been in the spotlight. A linear motor is a motor which effects linear movement instead of rotational movement by linearly extending a structure of a rotary-type motor. In the case of a linear motor car, a magnetic field is produced by supplying alternating current to a primary coil mounted on the car side, and a force is generated due to an interaction between this magnetic field and a magnetic field produced on a secondary coil (reaction plate) mounted on the track side. This force is utilized as a motive force. Thus, a driving force of the linear motor car is obtained.
The reaction plate is required to have a property of low electric resistance as an essential condition. In this relation, copper or copper alloy is suitable for a reaction plate material. However, if copper or copper alloy is used alone, the cost is too high, and the strength is insufficient. These are the reasons why a reaction plate composed of a copper or copper alloy material and a steel material of high strength is used generally. This composite structure is obtained by hot rolling bonding (hot bonding) in which a copper plate or a copper alloy plate and a steel plate are placed on each other and rolled, or by explosive bonding.
The conventional manufacturing method of the composite material involves the following disadvantages: (1) special equipments and devices are required for hot bonding or explosive bonding thereby raising the manufacturing cost; (2) hot bonding demands a high reduction; and (3) smoothness of the surface of products by explosive bonding is inferior so that cutting work of the surface is necessary.